A state-changing hydrogel composition means a hydrogel material, which contains a great quantity of water, and is suddenly transformed into a fluid state at a certain temperature.
In recent years, skin treatment using hydrogel has been applied in many areas such as cosmetic products, skincare, dermal beauty and dermal therapy. Hydrogel is well known as a material suitable to be used as a matrix for the controlled release of drugs (N. A. Pappas Ed., “Hydrogels in Medicine and Pharmacy, Vol. 11; Polymers”, CRC Press, Inc., 1987). This means that hydrogel as the matrix is used as a drug delivery body containing hormones such as progesterone therein to slowly release the hormones into the body, thereby controlling the quantity of the hormones. U.S. Pat. No. 5,344,655 by Sakai et al. discloses a technology of transdermally delivering drugs into the body using a hydrogel matrix containing water soluble polymers such as cellulose derivatives. In U.S. Pat. No. 5,405,366 by Fox et al., the use of adhesive hydrogel which forms an optical bridge and contains water soluble polymers in a transdermal drug delivery system is disclosed. U.S. Pat. No. 4,593,053 by Gebner et al. discloses the usage and production method of hydrogel that is friendly to skin and pressure sensitive. Transdermal delivery of drugs is a technique that transfers hormones such as Progesterone, Progestin, Estrogen, and Testosterone into the body through the skin. This sophisticated medicating system slowly and transdermally releases the predetermined quantity of medicine from hydrogel which adheres to the skin into body. U.S. Pat. No. 6,214,374 by Shumiller et al. introduces a composition of hydrogel for efficient transdermal delivery of drugs without being blocked by the skin, and a method and a device for producing the same. U.S. Pat. No. 5,064,654 by Verner et al. also discloses a composition of adhesive hydrogel for the transdermal delivery of drugs. U.S. Pat. No. 4,942,158 by Sapota et al. discloses a composition of hydrogel that contains a permeation enhancer for improved transdermal delivery of drugs. Moreover, U.S. Pat. Nos. 6,361,790 and 6,406,712 by Rolf et al. disclose a method of applying a dressing and a patch to the skin using hydrogel.
In all of the above conventional techniques, hydrogel is applied to the skin, but hydrogel only has a function of slowly releasing the drugs contained in hydrogel, acting as a matrix to the skin, while it is maintained in a gel state.
Meanwhile, when the drug delivery to the skin is controlled while hydrogel is kept in the gel state, there are inevitable disadvantages, namely, that it takes a relatively long time for the drugs to permeate through the skin, and that the drugs are delivered only to the portion of the skin with which the hydrogel comes into direct contact. Conventionally, every possible effort was made to add a permeation enhancer to hydrogel or to produce hydrogel that is friendly to the skin so as to overcome the disadvantages.
Generally, unlike medical treatment of a skin wound, when cosmetic products are used for skincare, a protection device must not adhere to the skin for a long time, but for a short period and subsequently be removed. Hydrogel is used to improve the effectiveness of skincare, and is produced in a form of a sheet or a patch to be effectively applied to the skin. However, even though the above hydrogel products are employed, if hydrogel is in a gel state, there is a limit in communication between hydrogel and the skin, and thus, it is impossible to assure a desirable quantity and speed of a cosmetic delivered from hydrogel to the skin.
Communication between hydrogel and the skin greatly affects the delivery of cosmetics or drugs contained in hydrogel to the skin. In other words, greater communication brings about easier and faster delivery of the cosmetics or drugs from hydrogel to the skin, but lesser communication causes less effective and slower delivery.
Furthermore, when hydrogel containing cosmetics is used for skincare, hydrogel adhering to the skin must be removed within a relatively short time in comparison with use of medical drugs for treatment, and thus, it is required that the cosmetics be rapidly delivered to the skin. In other words, the cosmetics contained in hydrogel applied to the skin for skincare must be quickly delivered from hydrogel to the skin in a great amount. To fulfill this feature, hydrogel must have a characteristic capable of quickly and uniformly delivering the cosmetics into the skin unlike conventional hydrogel, and thus, there remains a need to develop innovative hydrogel that can fulfill the above characteristics.